i am planning to use this smart solenoid driver http://www.st.com/web/en/resource/technical/document/datasheet/CD00000110.pdf
but i am uncertain how to use the maple's spi library to communicate with this chip
can anyone take a look at the documentation and tell me which mhz, which mode etc to select?
thanks so much.
stephan
mlundinse
Member
Its all in the datasheet so its good to practice how to read them, sure
they can be anything from clear and easy to understand to completly confusing
and filled with errors.
You will not be sure until you have tried it out, but from what I can see
it is MSB, clock idling low, data capture on first clock transition, that would be
Spi Mode 0, and max clock frequency of 2MHz.
The maximumum clock frequency also depends upon the amount of noise in the system
and length and capacitance of connecting leads. So start with a low clock and
increase it. If you have an oscilloscope you can watch the waveforms as you increase
spi clock frequency.
gbulmer
Moderator
stephanschulz - It might be helpful to add that that device appears to like a nominal 5V power supply.
At that voltage, its spec says its input pins would like a minimum of 0.7*5V = 3.5V.
It's signal pins could be driven directly at a slightly lower voltage, e.g. a Maple output pin. Certainly try it, but it might be a bit sensitive to electrical noise.
So the pins could be driven by 5V tolerant pins, using pull-up resistors to reach 5V, and set up with pinMode OUTPUT_OPEN_DRAIN.
AFAICT, the SPI input signals need to rise and fall reasonably quickly (i.e. 200ns), so relatively small pull-up resistors would be needed.
Some of the Maple SPI pins are not 5V tolerant.
So, for example D11 (SPI MOSI) and D13 (SPI SCK) are not 5V tolerant, and if they have a bit of a problem driving that chip directly, they couldn't be pulled up to 5V with pull-up resistors.
D32 (SCK) and D34 (MOSI) might be better because they are 5V tolerant, so you could try directly driving L9822 pins, or using pull-up resistors.
It looks like all the SPI signals need have 'slower' rise time, or fall time than 200ns.
The Maple GPIOs are normally set up for a 50MHz rise/fall, so if there are problems, it might be worth having a look at gpio_set_mode and setting the rise/fall time a bit slower.
For example GPIO_CR_CNF_OUTPUT_OD | GPIO_CR_MODE_OUTPUT_10MHZ or even GPIO_CR_CNF_OUTPUT_OD | GPIO_CR_MODE_OUTPUT_2MHZ`
WARNING: I've never tried this!
The L9822 looks very tolerant to being driven at low speed. AFAICT, it has no lower speed.
So you could write a simple 'shift_out' function using two digital pins, and just setting them with digitalWrite. This might be useful if you haven't got an oscilloscope, or have problems with SPI. Using a 'soft-SPI' would allow the bits to be written so slowly that LEDs could be wired up the the soft-SPI-equivalent signals, or print/println could be used, and you could see what is happening. The pins would be set up for pinMode OUTPUT_OPEN_DRAIN.
A small aside; that chip could be 'emulates' using an ordinary, cheap 8bit SIPO shift register ($0.50) driving LEDs. Judicous choice of part would work at 3.3V too, so you could do software development and testing without a 5V power supply.
Tiny aside: the L9822 is listed as obsolete e.g. a Mouser, but the L9822E is active, so I assume that's the part about to be used.
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